Method of and apparatus for amplifying and projecting sound waves



June 16, 1931. M. R. HUTCHISON METHOD OF AND APPARATUS FOR AMPLIFYING AND PROJECTING SOUND WAVES Filed Jan. 9; 1929 2 Sheets-Sheet l INVENTOR j fc'ller Reese Huick aLsonx.

BY i C ATTORNEY June 16, 1931- M. R. HUTCHISON METHOD OF AND APPARATUS FOR AMPLIFYING AND PROJECTING SOUND WAVES Filed Jan. 9, 1929 2 Sheets-Sheet 2 NV EN TO R Miler Reese Ha $051550 ATTORNEY Patented June 16, 1931 R um STATES PATENT. OFFICE f KILLER. BJEEBEEUTCHISON, OI LLEWELLY N PARK, WEST ORANGE NEW m, A!-

SIGNOB T NHODOH, INC; 0] W181 ORANGE, NEW JERSEY, A. GOD-PORTION OI nanawanr:

im-non or m APPLE-A118 I on amrrrme am) rnomorme sotmn wavm Application fled January 9,1829. Serial Io. 381,343.

My present invention is primarily concerned with'amplifying and projecting sound waves fromre roducers such as are commonly used for p onographs and radio, but it" will be obvious that the principles of m invention are applicable to sound waves rom other sources. v V I My invention is based upon the discovery that sound waves may be improved in quality b projecting them through a tortuous amp ifier in WhlCh the waves are reflected many times, preferably at substantially right angles, and that this may be accomplished without appreciably damping or distorting B waves of the more uniform or musical frequencies, yet with a material dampening,

wearing out and mufiling of waves of'irregular or' noise frequencies. The result is a sweetenin and purification of the sound.

For suc purpose, I prefer thatthe amlifying conduit have non-resonant walls,

ecause resonant amplifiers have a tendency to impose their own frequencies upon the sound waves which ass therethrough, thereby disproportionate l ing certain tones.

As the result of my discoveries, I have devised an amplifying means and method which assures the sweet, true amplification of musical sounds, the sound waves of regular frequencies being truthfully amplified without distortion, while the sound waves of irregular frequencies, such, for instance, as needle noises and other noises introduced by mechanical defects in the recording or reproducing apparatus are subdued in the amplifying pro ector.

In accordance with the preferred embodiment of the invention I provide an amplifier consisting essentially of two spaced parallel non-resonant walls, affording a tortuous pathway for the sound waves formed by articulating reflector surfaceslon theo posed faces of the discs. Such surfaces may conveniently formed by deep concentric corrugations or grooves in the opposed disc faces.

Where longer air columns are required for relatively deep-toned amplifiers, the disc corrugations may be supplemented by articulating concentric partitions on the discs. These y and unduly magnify range of musical notes an partitions produce a radially labyrinthine air column of any desired length including a plurality of connected annular l The deflector surfaces direct the waves flf om one leg of the column into the next without distortion; Wave front ex ansion occurs only as the wave front is de ected from the end of one column leg into the next one. During the passage of the waves through the column legs, at right an Ice to the radius, no expansion occurs, so t at I have in effect an desired length of labyrinthine air co umn through which sound'waves of regular frequency are propagated without distortion or.

muflling while being continuously confined against lateral expansion in one direction and intermittently expanded at predetermined intervals in the other direction, the

amplification bein accompanied by the subthing of undesira 1e noises.

The column 1e serve in each instance to more or less rea ign andreun'ite the wave front and direct it at a true 45 angle against the next defiectin nature of the charm r sections where expansion occurs permits such expansion at the maximum rate of speed during the ex ansion cycles or in other words at a rate w ich equals the propagation rate multiplied by 21! The path followed by the reflected waves, that is, the effective air column le h, is twice the straight line distancefrom t e entrance to the exit of the projector, plus the lengths of the partitions, when the latter are used. Where no partitions are used, at least one-half of the len h of wave front travel will be in a non-ra ial (non-expanding) direction and the expansion is in effect intermittent, although there is no opportunity to mechanically realign or redirect the wave front between successive deflecting surfaces.

The discs may be made of heavy material, such, for instance as cast metal, so that their natural frequencies are be 0nd the normal sympathetic vibration producing audible resonance will not be set up in them b the vibrating air column which they con ne. They may be stamped from heavy sheet metal and their 1 surface. The annular corrugated backs filled with plaster of Paris or the like.

The tortuous conduit, passageway or amplifying chamber which is provided by the opposed faces of the discs or by such faces in combination with the labyrinthine partitions, not only provides a series of wave reflecting surfaces which wear out and damp out the undesirable waves or irregular freuencies but materially assists in loading t e diaphragm or other propagating element, since the load of an alr column in a tortuous chamber excee s load of a column of similar length in a straight chamber. These corrugations and artitions furthermore control the ratios 0 total wave front expansion to total distance of wavepropagation, and this seems to be an important factor in effectively loading or cou ling the air column to the diaphragm for efhcient air wave generation and propagation, particularly with respect to the longer wave lengths.

The invention may be more fully understood from the following description in connection with the accompanying drawings, wherein:

Fig. 1 is a transverse sectional view through a non-resonant amplifier embodyin the invention;

Fig. 2 is a reduced front elevational view thereof with parts of the front disc broken away;

Fig. 3 is a fragmentary view similar to Fig. 1, but illustrating a slight modification;

ig. 4 is a view similar to Fig. 1 and illustrating a further modification;

Fig. 5 is a partial front elevational view of the amplifier shown in Fig. 4, and with parts broken away and in section for clearness.

In Figs. 1 and 2, I have shown a comparatively simple elementary embodiment of the invention, in which a pair of spaced, parallel non-resonant discs 10 and 11, cooperatively define the amplifying chamber. These discs are preferably of fairly heavy cast metal construction. Disc 11 has an opening 12 at its center constituting a throat through which sound waves from any ordinary electromagnetically actuated iaphragm reproducer unit such as 13 are directed into the center of the amplifying chamber. Radially beyond the disc 10, the disc 11 is provided with a bell or flare 22 serving as a mouth piece to properly direct the amplified sound waves which issue radially from between the disc edges. Spider legs 30 projecting inwardly from horn 22 support disc 10 in proper position.

The opposed faces of the two discs are annularly ribbed or corrugated with a series of equi-distantly spaced, regular corrugations 10a and 110, these corrugations considered cross-sectionally havin right angular apices and defining grooves etween them of similar crosssectional shape. The corrugations of one disc alternate and articulate with those of the other, all corrugation apices being preferably in the same plane so that the exposed disc faces cooperatively define a regularly-tortuous, circular amplifying chamber through which sound waves entering centrally from the throat 12 are rad1al ly propagated, their wave fronts expanding 01rcumferentially only. Each successive rib face is in position to intercept and deflect through 90, to the next face, the direct reflections from the preceding face.

In the course of their travel from the center of the chamber to the outer periphery thereof, the waves will be reflected back and forth striking against all of the deflecting surfaces which are formed by corrugations 10a and lie, the axis of travel of the waves being indicated in dotted lines in Fig. 1. Such minor parts of "the waves as are not intercepted at the 45-degree angle will be subject to progressively confusing reflections and will be dissipated. The path of travel of the orderly reflection, in passing from the center to the outer edge of the chamber, is

twice as long as the distance which would be traveled if the faces of the discs were uncorrugated and the waves could travel in a straight line, half of the wave travel being non-radial and non-expanding.

The most rapid wave front expansion obtainable between parallel surfaces is circular expansion, which is approximately 6 to 1. For instance, if circular. the expansion chamber of F l is 12 inches in diameter, then without acting surfaces, a sound wave in traveling 6 inches from the disc center to the disc edge would have expanded to approximately 36 inches, but with the deflecting surfaces, the refiected wave must. travel 12 inches to expand to 36 inches, an overall ratio of approximately 3 to 1. The expanding part of this travel, however, is only 6 inches and is at the same rate as if there were no reflections, namely, 6 to 1. is that the air column length is twice as great and the multiple reflections have the desired smoothing efi'ect on the waves. Thus the 3 to 1 ratio is merely a distance ratio, not a speed ratio and the distance ratio controls primarily the diaphragm air-column load. This may be considerably increased without in any way varying the preferred maximum expansion ratio of 6 to 1, or any other ratio which may be arbitrarily selected, as by making the passage semicircular or following the surface of a cone.

In Fig. 3, I have illustrated a slight modification in which discs 10b and 11b corresponding to the discs 10 and 11 are similarly arranged to form an amplifying chamher. In this case, instead of using right angular corrugations, I utilize semi-circular grooves 14 properly articulated to give the equivalent of 2 right angular deflections, the total of which is 180 degrees, while preserv- The difference ing a chamber of uniform'width' throughout. Throat 12a and horn 22a corresponding to throat and horn 12, 22 of Fig. 1 are retained. Here the axis" of wave travel is substantially the same as the wave travel illustrated in Fig. 1, but the surfaces not being plane, the flanks of the wave front, make the 180 degree turns by many small angle reflections. The rounded grooves give a somewhat more mellow rolling tone to music than the angular grooves, but the latter give better artlculation. In Figs. 4 'and'5, I have shown a modification which permits the use of a considerably longer air column without radially increas' ing the size of the amplifier. The distance ratio of expansion to propagation has been changed from approximately 3 to 1 to ap proximately to 1, yet at the places where expansion occurs, the ratio of expansion to propagation remains the same, about 6 to 1. In this form of the invention, a pair of relatively widely spaced non-resonant discs 10c and 110 are provided, these discs being conveniently stamped from some hea outer sides filled with plaster of Paris or equivalent material 16 which militate-s against resonance. The corrugations in the discs are similar to those shown in Fig. 1 and at the peak of each corrugation there is provided a non-resonant circular wave-guiding partition 17 adapted to enter between and properly articulate with the similar artitions of theopposite disc. Throat 12 and bell 226 corresponding to the throat and bell.12,- 22"of Fig. 1. are retained and legs 30a support disc 100 from the horn 22b.

Inasmuch as squeezing ofthe air column at any point is to be avoided, I prefer to make the entering throat 12b of the amplifier of a cross-sectional area which is at least as small as the cross-sectional area of the first annular leg orportion of the amplifying chamber into which the wave front is directed. A similar condition is true in Figs. 1 and 3, in that the total cross-sectional area of the throat 12 or 12a is no greater than the annular cross-sectional area of the amplifying chamber at the point where the amplifier chamber and throat communicate.

WVith this form of the invention, I have provided a radially labyrinthine amplifying passage, the labyrinth being formed by a series of concentric serially connected annular ortions, the combined length of which is eterminative of the total air column length of the amplifier. The sound waves in passing from the center of the chamber to a point of discharge at the outer end of the chamber are, during the major portion of their travel sustained against expansion in any direction. As they are deflected from one leg of the labyrinthine chamber into the next leg thereof expansion occurs and it will material and having the corrugations in their be seen that the non-radial or non-expanding travel cycles of the wave front greatly exceed the radially propagating and expandin cycles. N

e principal difference between Fig. 1 and Fig. 4 is the fact that the latter figure shows a construction with a longer air column and consequently an amplifier better adapted to project longer sound waves,,characteristic of lower frequencies. Moreover, the diffused and irregularly reflected parts of the waves are more completely subdued. The sound cannot short-circuit radially from the entrance to the exit. The clarity and truthfulness of the amplified sound and the subduing of undesirable noises is common to both constructions as is the actual rate of wave expansion.

Air column length may be increased or decreased without corresponding increase or decrease in the number of reflecting surfaces employed or the size of the amplifier, by simply. varying the length of some or all of the partition walls 17.

Air column length is an important factor primarily because it controls the dominatmg tonal quality and the sonority of the amplifier and is an importaptfactor in controlling the loading of the diaphragm. That is to say, an-ordinaryreproduceidiaphragm without any projector is'extremely inefiective, apparently because the waves are radiated directly and the wave front expands as the square of the distance of propagation. The sound roduced is surprisingly weak because the an is not properly confined, or, so to speak, loaded onto the diaphragm. The circular expansion between confinin surfaces giving a 6 to 1 expansion is insu cient for the pur se. By the present invention, I accomplis the desired circular expansion at intervals and utilize the non-expansion intervals to increase air column length and the diaphra load. It will thus be seen that the diap ii i agm loading while depending, of course, to a certain extent on the total length of the air column is even more directly dependent upon the distance ratio of wave propagation to wave front expansion and that the present invention enables me to combine the desirable maximum expansion rate of the wave front without any corresponding loss in the effective diaphragm loading.

The damping out of the irregular or noise frequencies seems to depend much less on air column length than on the number of reflecting surfaces against which the waves are caused to impinge. This factor of the number of reflector surfaces used is also capable of arbitrary predetermination without regard to air column length either by using smaller ribs on more closely spaced confining discs, or larger ribs with greater spacing, or by using a greater or less number of partitions to make air column legs of any desired length.

So long as the wave reflections are at right angles or substantially at right angles, tonal quality of the amplifier seems to be variable independently of the number of reflecting surfaces used and to be directly proportional to the effective air column length. In other words, even a very great number of right angular reflections seem inoperative to deaden or distort waves of regular frequencies.

From the foregoing, it will be seen that a desirable embodiment of the invention involves the use of an amplifying conduit which confines the wave fronts against'expansion in one dimension and permits their circular expansion in the other dimension, at intervals and for distances required to afford a total air column of suflicient length to give the desired tonal qualities together with means for right angularly deflectin the waves in their course of travel throng the conduit whereby undesirable noises are subdued without detriment to sound waves of regular frequencies.

As pointed out above, by the proper design of the apparatus, the air column length and the number of deflecting surfaces can be varied independently of each other. The rate of the wave front expansion, where there is any, is a constant factor, but the frequency and length of the expansions is subject to variation entirelyindependently of air column len h. In this connection, for instance, I mig t simply radially extend the two discs of Fig. 1 until they confined an air column equal to the total air column length of Fig. 4. I would thus have a number of expansion zones far greater than those permitted by the device of Fig. 4 and yet have the same air column length and consequently the same tonal quality and sonority.

While I have discussed throughout the use of an amplifying chamber of general circular form which permits radial wave propagation accompanied by circular wave front expansion intervals, it is within the s irit of the invention to utilize amplifying c iambers of less than circular shape, for instance, of semi-circular or sectoral shape. When such chambers are used, it is never possible to obtain maximum rate of wave front expansion and a sectoral chamber must be of considerably longer radius than a circular chamber in order to accomplish expansion of the wave front to a similar extent. On the other hand, with a sectoral chamber only the curved side of the chamber will be open and I will have in effect a four-walled amplifier which of course facilitates diaphragm loading. When the column is confined on four sides instead of two, the ratio between wave propagation and wave front expansion becomes a much less important factor in the final determinachamber which permits no expansion. In

this instance, the only factor other than air column length which would be determinative of diaphragm loading would be the added frictional resistance to wave motion which is an incident of the undulations or corrugations in the chamber walls.

I claim:

1'. A method of amplifying sound which consists in propagating sound waves from a center through a tortuous conduit, repeatedly right angularly reflecting the wave while circularly expanding it in one dimension, at intervals and preventing expansion thereof in the other dimension.

2. A method of sound am lification which includes propagating soun waves radially through a conduit having a circumferential open mouth, repeatedly reflecting the waves at right angles during the course of their passage through tfie conduit and intermittently circularly expanding the waves in one dimension only.

3. A method of amplifying sound which includes passing the sound waves through an open mouthed conduit which is continuously expanding in one dimension only and repeatedly deflecting the waves at right angles during the course of their passage through the conduit.

4. A method of amplifying sound which consists in propagating sound waves through a conduit, preventing expansion of the wave front in one dimension, intermittently radiallg expanding it in the other dimension, and de ecting the wave front at right angles at least once between each expansion cycle.

5. A method of amplifying sound which consists in propagating sound waves through a conduit, repeatedly reflecting the wave front at substantially right angles and alternately permitting and preventing wave front expansion in one dimension only between consecutive deflections.

6. A sound am lifier including a pair of spaced parallel iscs, each of heavy nonresilient cast metal, one disc having a central opening therein through which sound waves enter the space between the discs, and means on the opposed disc faces coacting to define a radially tortuous passageway through which the waves are radially propagated and circularly expanded.

7. A sound amplifier including a pair of spaced parallel discs, each of heavy non-resilient cast metal, one disc having a central opening therein through which sound waves a "r "3, till till . define a through which the waves are propagated,

enter the space between the discs, and means on the opposed disc faces coacting to define a radially tortuous passageway through which the waves are propagated, said means comprising alternating annular concentric and grooves on one disc registering with similar ribs and grooves on the other disc.

8. A sound amplifier including a pair of spaced parallel discs, each of heavy non-resilient cast metal, one disc having a central opening therein through which sound waves enter the space between the discs, and means on the opposed disc faces coacting to define a radially tortuous passageway through which the waves are propagated, said means bafilin straight radial propagation of the wave i ront and causing it to travel in a regularly repeated series of right angular deflections.

9. A sound amplifier including a pair of spaced parallel discs, one disc having a central opening therein through which sound waves enter the space between the discs, and means on the opposed disc faces coacting to radially tortuous passageway said means bafiiing straight radial propagation of the wave front and causing it to travel in a regularly repeated series of right angular deflections, which are alternately in radial and non-radial directions, whereby the wave front is intermittently circularly expanded in one direction.

it), A sound amplifier including opposite walls the opposed faces of which form parallel surfaces of revolution and define a radially expanding passage, a central opening in one of said walls through which sound waves are introduced, said walls preventing wave ext pansion in one direction and their opposed faces providing alternating concentric circular ribs and grooves, the ribs and grooves of one wall registering respectively with the grooves and ribs of the other, and all of the rib apices lying in common surface of revolution parallel to the planes of the walls.

1].. A. sound amplifier including opposite walls the opposed faces of which form parallel surfaces of revolution and define a radially expanding passage, a central opening in one of said walls through which sound waves are introduced, said walls preventing wave expansionin one direction and their opposed faces providing alternating concentric circular ribs and grooves, the ribs and grooves of one wall registering respectively with the rooves and ribs of the other, and all of the 

